U.S. Pat. No. 6,544,083, which is incorporated herein by reference in entirety, discloses a gear shift mechanism in which a cam structure comprises a protrusion that is shaped to extend into a channel formed in a cam follower structure. The cam follower structure can be provided with first and second channels that allow the protrusion of the cam to be extended into either which accommodates both port and starboard shifting mechanisms. The cam surface formed on the protrusion of the cam moves in contact with a selected cam follower surface formed in the selected one of two alternative channels to cause the cam follower to move axially and to cause a clutch member to engage with either a first or second drive gear.
U.S. Pat. No. 6,817,461, which is incorporated herein by reference in entirety, discloses a clutch mechanism for changing gear in a marine propulsion system having a cam member that is rotatable about a first axis in coordination with the rotation of a shift shaft. A cam follower is associated with the cam member and supported for axial movement along a second axis. The cam follower is provided with cam follower surface segments that cause the cam follower to move axially in a direction parallel to the second axis in response to rotation of the cam member about the first axis between first and second rotational positions. Further rotation of the cam member from the second rotational position to a third rotational position causes no further movement of the cam follower because of the shape and position of cam follower surface segments that allow continual contact between the cam member and the cam follower while allowing rotation of the cam member without associated axial movement of the cam follower.
U.S. Pat. No. 8,435,090, which is incorporated herein by reference in entirety, discloses a marine drive comprising a gear case housing a vertical drive shaft that rotates a generally horizontal propulsor shaft in a forward direction upon operational engagement with a forwardly rotatable gear and rearward direction upon operational engagement with a rearwardly rotatable gear. A lubricant exclusion cover is disposed between the forwardly and rearwardly rotatable gears so as to limit churning of lubricant by at least one of the forwardly and rearwardly rotatable gears.
A variety of shift mechanisms for changing gear in marine propulsion systems exist in the prior art, examples of which are described in the above-referenced U.S. patents. In some examples, a device that is commonly referred to as a bell crank mechanism has high efficiency, but does not provide a dwell function to allow for over-travel. In other examples, a device commonly referred to as a desmodromic mechanism is a cam that is constrained in size, which leads to high pressure angles and low mechanical efficiency.